It took me a full 3/4 of the way through this book before I found a decent story. Most of the stories suffered from one or more of the following: 1) could have been set anywhere remote. The particulars of the Severn Valley locale played no role in the story. Have these authors even read anything by Ramsey Campbell? 2) bizarre or disjointed writing styles that only detracted from the plot 3) non-endings or endings that did not follow from the story. In several of the stories it seemed as though the author decided it was time to go to the pub and just wrote anything to end the story (or came back from the pub and finished drunk).
I liked Szymanski's "Random Access" as a nice expansion of "The Insects from Shaggai" with a computer program saving the day. Robert Price has a decent piece, if you can ignore a gaping hole or 2 in the story line. Campbell's own contribution is fine, and is perhaps the only story to actually USE the Severn Vally mythos and expand upon it in any significant way. C.J. Henderson's piece is also good and happily can be found in the fine anthology "The Occult Detectives of C.J. Henderson" so you don't need to buy this book to read it.
I'd recommend this book only to folks like me who just have to buy all of the "Call of Cthulhu" books for their collection. Feel free to buy it and put it on your shelf unread, you will be missing very little. Then go read some Campbell and Henderson elsewhere.